BaSb(H2PO2)3Cl2: An excellent UV nonlinear optical hypophosphite exhibiting strong second-harmonic generation response

Non π-conjugated tetrahedral groups have emerged as potential basic modules for developing ultraviolet (UV) nonlinear optical materials. However, their intrinsic weak hyperpolarizability and small polarizability anisotropy severely restrict the performance of the designed material. Herein, the first antimony hypophosphite, BaSb(H2PO2)3Cl2, was successfully synthesized via rational design, which exhibits superior nonlinear optical properties including strong second harmonic generation response, appropriate birefringence and wide transmittance, indicating it is a potential UV nonlinear optical material. Remarkably, the title compound exhibits the largest nonlinear optical coefficient (5 × KDP) among all reported antimony-based oxyacid compounds. Detailed theoretical calculations confirmed that its excellent nonlinear optical properties are primarily derived from the ordered [Sb(H2PO2)3Cl2]2- anionic clusters composed of [H2PO2]- pseudo-tetrahedra and [SbO3Cl2]5- distorted polyhedra. This work would extend UV nonlinear optical material system to hypophosphites and lead the further inquiry of new structure-driven functional materials.